A wind power plant usually has a plurality of wind turbines for converting wind energy to electricity. To supply electricity to the electricity end users, the wind power plant is connected to a power grid. However, before the wind power plant can be connected to a power grid, the wind power plant has to meet the requirements of electrical performance of the wind power plant specified by grid codes. One requirement is an initial response time of the wind power plant. Generally, the wind power plant has a wind power plant controller which monitors a power grid voltage and compares the power grid voltage with an external setpoint. A difference between the actual power grid voltage and the external setpoint (e.g. an error signal) is used to calculate a command for reactive power production for the wind power plant. This command is sent from the wind power plant controller to the individual wind turbines which in turn will respond (e.g. produce more or less power in order to adjust the power grid voltage) upon receiving the command. The error signal may be caused by a change in the actual power grid voltage or a change in the external setpoint. The initial response time of the wind power plant is to be understood as the time period starting upon detection of a change in the power grid voltage or a change in the external setpoint and ending as soon as the first wind turbine of the plurality of wind turbines of the wind power plant responds (as soon as response is detected).
For example, as shown in a graph 500 of FIG. 5, the British grid code requires an initial response time of not more than 200 ms. That is, the first wind turbine of the wind power plant is required to respond at a time of not more than 200 ms after the time a change in the power grid voltage or a change in the external setpoint takes place, based on the reception of respective control data. The remaining wind turbines of the wind power plant subsequently respond, also based on respective control data. The British grid code requires that, after 1 s, the reactive power production of the wind power plant must be greater than 95% of the required response 502 (e.g. reactive power production).
Generally, control data is sent to a wind turbine only after information about all wind turbines has been collected, the collected information has been processed and the control data for all the wind turbines has been prepared to be sent out. Therefore, the total time for collecting the information about the wind turbines, processing the collected information and generating the control data for all the wind turbines might not meet the requirement of the initial response time specified by the grid codes.
Hence, one objective of the present invention is to avoid the above-mentioned problems.